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WAEC Mathematics 2018 Paper

Question : 49

Total: 50

\cap

Solution:

Concept:

Use the set relation

n(M\cup N)=n(M)+n(N)-n(M\cap N)

, because elements common to both sets are counted twice when the individual sizes are added.

Explanation:

Let

n(M\cap N)=x

Substitute the given values:

40=20+30-x

40=50-x

Hence

x=50-40=10

Thus 10 elements belong to both

M

and

N

Answer:

n(M\cap N)=10

So the given options do not contain the correct answer as printed.

Option D would correspond to

n((M\cap N)')=38

, not to

n(M\cap N)

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